What We Know About Fourth Covid Vaccine Doses—Including If We Might Need One

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Robert Hart   Forbes U.S. Staff

What We Know About Fourth Covid Vaccine Doses—Including If We Might Need One

Photo: Pfizer Inc. Twitter

The increasing number of Covid-19 infections reported in people who are fully vaccinated and boosted has prompted some governments to launch campaigns to give their citizens a second booster shot, though experts disagree as to if, and when, it might be needed. 


- Health officials in Israel recommended a fourth shot of the Moderna or Pfizer-BioNTech coronavirus vaccines for all adults, citing early data from the country’s health ministry showing a fourth dose doubled protection against symptomatic illness and gave three-to-five times the protection against serious illness, compared to three doses.

- The findings conflict with other preliminary research from Israel—which indicates another booster may not be enough to protect against the omicron variant—and experts disagree as to whether the fourth shot will be needed at all. 

- Vaccine makers, including Pfizer and Moderna, have said additional boosters may be needed in light of the omicron variant and as protection against symptomatic infection wanes over time, though Pfizer CEO Albert Bourla noted more data is needed to see whether three doses are enough. 

- While early data suggests protection against symptomatic disease wanes within weeks of the third shot, new studies found the vaccine still offered strong protection against severe illness and hospitalization, which experts say is the most important reason for vaccination.     

- The European Medicines Agency and the World Health Organization have both warned frequent boosting is not a sustainable long-term strategy and the U.K.’s Joint Committee on Vaccination and Immunisation said additional boosters are not yet needed as the first set are still providing strong protection.

- Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told Forbes there is not much data showing a fourth dose adds to the protection of a third dose and there may be “diminishing returns” with continued boosting using the same vaccine formula.


Though Israel could become the first country to offer all adults a fourth Covid-19 shot, many nations, the U.S. included, already offer a fourth shot to people with compromised immune systems. For immunocompromised people, the third shot is considered part of the initial course of vaccinations and not a booster.  


Omicron-specific vaccines. Most major vaccine makers are developing shots targeting the omicron variant, which is able to skirt the immune defenses provided by previous infection and vaccination. Pfizer and BioNTech began clinical trials for their shot on Tuesday and Moderna, Johnson & Johnson, AstraZeneca and Novavax are all among vaccine makers developing the targeted shots. Pfizer and Moderna, whose vaccines are made using swiftly edited and manufactured mRNA technology, say their omicron-specific shots can be ready as soon as March. 


What is fully vaccinated. With two shots providing relatively little protection against omicron, governments and businesses are grappling with whether to include booster shots in the definition of “fully vaccinated,” a distinction that could have important ramifications for vaccine mandates and requirements. Several European countries have made boosters mandatory for tourists and France has required holders of vaccine passes, needed to access most public spaces, to get a booster shot within four months of their second shot to keep their pass. The U.S. Centers for Disease Control and Prevention is taking a more hedged approach and is keeping boosters out of its definition of “fully vaccinated.” Instead, it will just consider Americans “up to date” with their Covid-19 vaccinations if they’ve had the booster when eligible.

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Robert Hart   Forbes U.S. Staff

I am a London-based reporter for Forbes covering breaking news. Previously, I have worked as a reporter for a specialist legal publication covering big data and as a freelance journalist and policy analyst covering science, tech and health. I have a master’s degree in Biological Natural Sciences and a master’s degree in the History and Philosophy of Science from the University of Cambridge.